Seat for the school head, also a pupil (5)
I believe the answer is:
stool
'seat' is the definition.
(I know that seat can be written as stool)
'school head also a pupil' is the wordplay.
'head' indicates taking the first letters.
'also' becomes 'too' (synonyms).
'a pupil' becomes 'l' (as in a learner driver with L-plates on their car).
The first letter of 'school' is 's'.
's'+'too'+'l'='STOOL'
'for the' is the link.
(Other definitions for stool that I've seen before include "Backless chair" , "Simple seat" , "Armless seat" , "Seat without a back" , "Three-legged backless seat" .)